Annular flow heat exchanger

ABSTRACT

Gas of constant or widely varying temperature enters an integral plenum from which the gas is caused to flow radially. The radial flow alternates between outward and inward flow with short axial displacements between cycles which lead the gas to an integral outlet plenum. These flow paths are determined by transverse discs which act as heat transfer fins and baffles where required. A number of axial tubes which pass through the fins at right angles carry a cooling liquid which controls the temperature of these tubes and the transverse discs. As the gas flows along the surface of the fins and over the tubes it gains or loses heat until its temperature closely matches that of the liquid in the tubes, thus the gas exits the heat exchanger at a controlled temperature. This arrangement lends itself to an application where hot exhaust gas and ambient air are mixed as they enter the inlet of the heat exchanger. The gas mixture then flows around a number of axially spaced heat transfer fins in a path that includes radial and axial directions. This action thoroughly mixes the gases for sampling and analysis. The attachment of a positive displacement pump at the exchanger outlet maintains a constant mass flow of the gas mixture for quantitative determination.

United States Patent [1 1 Fegraus et al.

[451 May 20, 1975 1 1 ANNULAR FLOW HEAT EXCHANGER [75] Inventors: ClarkE. Fegraus; Jimmy G.

Sundahl, both of San Bernardino. Calif.

[73] Assignee: Automotive Environmental Systems,

Inc., San Bernardino, Calif.

[22] Filed: Feb. 12, 1973 [21] Appl. No.: 331,514

[52] US. Cl 165/145; 165/158 [51] Int. Cl F285 9/22 [58] Field of Search165/141, 145, 51, 157-161,

[56] References Cited UNITED STATES PATENTS 1,948,550 2/1934 Voorheis165/161 2,138,001 11/1938 Fluor, Jrv 60/320 3,700,029 10/1972 Thrun165/51 Primary Examiner-Charles Sukalo Attorney, Agent, or FirmMorrisLiss [57] ABSTRACT Gas of constant or widely varying temperature entersan integral plenum from which the gas is caused to flow radially. Theradial flow alternates between outward and inward flow with short axialdisplacements between cycles which lead the gas to an integral outletplenum. These flow paths are determined by transverse discs which act asheat transfer fins and baffles where required. A number of axial tubeswhich pass through the fins at right angles carry a cooling liquid 4which controls the temperature of these tubes and the transverse discs.As the gas flows along the surface of the fins and over the tubes itgains or loses heat until its temperature closely matches that of theliquid in the tubes, thus the gas exits the heat exchanger at acontrolled temperature.

This arrangement lends itself to an application where hot exhaust gasand ambient .air are mixed as they enter the inlet of the heatexchanger. The gas mixture then flows around a number of axially spacedheat transfer fins in a path that includes radial and axial directions.This action thoroughly mixes the gases for sampling and analysis. Theattachment of a positive displacement pump at the exchanger outletmaintains a constant mass flow of the gas mixture for quantitativedetermination.

6 Claims, 7 Drawing Figures PATENTED MAY 2 01975 SHEET 2 OF 3 ANNULARFLOW HEAT EXCHANGER FIELD OF THE INVENTION The present invention isrelated to a heat exchanger, which mixes two gases entering an inlet.More particu larly, the invention is related to a heat exchanger whichemploys liquid coolant to control the temperature of the gases whileinternal tube and fin heat exchangers facilitate high gas flow rates.The gases flow together through the exchanger via radial and axialdirections.

THE PRIOR ART In pursuance of the analysis of automotive emissions, itis imperative to achieve a constant mass flow of internal combustionengine exhaust gas and ambient air that is mixed with the gas such thatthe mass flow of the mixture is constant while the proportions of eithergas vary. The mix; are is cooled or heated by a heat exchanger asrequired to maintain a fixed outlet temperature and has an outlet thatshould deliver a constant density flow therefrom.

Because the temperature of this mixture may vary over a large range atthe inlet of the exchanger, but must be constant within a tolerance atthe outlet, the heat exchanger is called upon to perform an extremelyprecise heat transfer function. Previously available heat exchangerdesigns have not met these requirements. A primary deficiency in manypreviously tried heat exchangers comes about because these heatexchangers lack sufficient tortuous path directions to effect the mixingof gases as they are cooled by heat exchanger fins. Furthermore,previously tried heat exhangers lack the large surface area on the gasside of the heat exchanger to effect proper heat transfer. Those whichdo meet these requirements are invariably either too large or suffer toohigh a pressure drop in the flow of the gas.

The prior art, as exemplified by US. Pat. No. 2,625,l38, discloses aheat exchanger, and more particularly a stand boiler having annularaxially spaced baffles which causes water within the boiler housing totraverse a symmetrical path between the baffles. The path includesalternating radial and vertical directions for producing greater thermalefficiency and a considerably more even temperature distributionthroughout the body of heated water. Vertical fluid tubes pass throughthe baffles to promote heat exchange. The design exposes hot gas to thesmaller inside surface area of the tubes and water to the larger outsidearea. The design has no provisions such as fins or extended surfaceareas to increase heat transfer from the gas to the tubes which areexposed to the liquid. It must be in a vertical position to operate.

Although the prior art, such as the mentioned patent, achieves desirableheat exchanger results, this type of exchanger does not provide forallowing the gas to flow radially over fins and the outside surface oftubes. Since heat transfer from a liquid to a tube is far more rapidthan from a gas to a tube, it is necessary to have an improved heatexhanger wherein the gas is exposed to far greater surface areaincluding fins than the liquid. Moreover, it is necessary to provide forthe mixing of two gases, namely ambient air and hot emission exhaust.Accordingly, an improved exchanger is required to achieve the improvedheat transfer for precise temperature control applications, and themixing and commensurate constant mass flow of mixed gases as required bypollution analysis applications.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present inventionincludes a heat exchanger having a symmetrical flow path withalternating radial and axial directions and may be oriented in anyoperating position. However, the heat exchanger not only includes theaxially spaced annular baffles but also fins which exchange heat duringradial flow and specially designed inlet means for causing simultaneousdelivery of air and emission exhaust gases. Further, the fin as semblywithin the exchanger provides for many divisions and blendings of thegas for promulgating mixture of the incoming gases. To insure that aconstant mass flow of air and internal combustion engine exhaust gasesis maintained, the heat exchanger has its outlet coupled to a positivedisplacement gas pump. The combination of these components achieve thedesired constant results. However, constant mass flow would be extremelydifficult to achieve were it not for the homogeneity of the air/exhaustmixture produced by the heat exchanger. Analysis of the gas requireshomogeneity also. Moreover, constant mass flow could not be achievedwithout constant pressure drop and outlet temperature. This precisetemperature control is augmented by provisions for symmetrical coolantflow and reverse flow where the coolant enters the end of the heatexchanger from which the gas exits. This feature is essential forprecise temperature control because the coolant temperature is affectedby further heat transfer with the gas as it travels through the heatexchanger. It is desirable to have the last interchange of the gas to bethe first interchange with the coolant whose temperature is controlledby other means.

In operation of the present invention, the radial flow heat exchanger isused to mix a varying proportion of internal combustion engine exhaustgas and clean ambient air whose mass sum is constant. The temperature ofthis mixture varies over a large range on the inlet end but must beconstant within a tolerance on the outlet end of the heat exchanger. Thegas flow pressure drop must be low, ideally less than 3 inches water,and constant. Since the mass of a gas is a function of the pressuretimes the volume divided. by the temperature, and a pump maintains aconstant volume, pressure divided by temperature must be held constantby the heat exchanger.

The present heat exchanger controls gas temperatures in two ways. First,the heat exchanger acts as a heat sink. Secondly, gas temperature iscontrolled by controlling fin temperature to regulate gas temperaturewith a controlled coolant temperature.

The inlet gases are mixed by an internal header adjacent the inlet whichacts as a mixing surface for the inlet gases. Further, the fins of theheat exchanger split gas into radially flowing discs which are blendedback into a flowing column and alternately, a flowing annulus. Thedesign of the heat exchanger interior is symmetrical so all these mixingfunctions are concentric and symmetrical about the axis of the heatexchanger thus assuring homogeneity.

A further advantage of the present invention is its capability to reducenoise propagated through the inlet ducting by a positive displacementgas pump coupled to the heat exchanger outlet. The particular finconfiguration in the heat exchanger interior prevents line of sightnoise propagation and provides volume changes which reflect noisepressure waves.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic block diagramillustrating the present heat exchanger in connection with pump meansfor achieving the desired constant mass flow of sampled gas.

FIG. 2 is a cross-sectional view of the heat exchanger exposing theinterior components thereof.

FIG. 2A is a cross-sectional view taken along section lines 2A2A in FIG.2.

FIG. 3 is an alternate sectional view illustrating the heat exchangeroperating in a single gas pass and single coolant pass mode with reverseflow.

FIG. 4 is a cross-sectional view taken along a plane passing throughsection line 44 of FIG. 2.

FIG. 5 is an additional alternate embodiment of the present inventionillustrating the coaxial alignment of two inlets and the outlet from theheat exchanger and a single gas pass.

FIG. 6 is still another alternate view that illustrates a reciprocalstructural relationship between inlets and the outlet as shown in FIG. 5and four gas passes to illustrate how easily the number of passes can bearranged.

DETAILED DESCRIPTION OF THE INVENTION Referring to the figures, and moreparticularly FIG. 1 thereof, reference numeral 10 generally indicates aconstant volume sampling system. A heat exchanger 16 which constitutesthe basis for the present invention,

has a first inlet 12 for delivering automobile exhaust gas to the heatexchanger 16. A second inlet 14 delivers clean air to the heat exchanger16. The exchanger mixes and controls exit gas temperature. Thetemperature conditioned gas mixture exits from the heat exchanger atoutlet 18. A positive displacement pump is connected to the outlet 18through pipe 20. A parallel pipe connection 22 allows directcommunication between the oulet I8 and a smaller sample pump 24 whichfills a sample bag 26 at a constant mass flow rate. The sample bag 26 isthen subjected to gas analysis to determine the pollution constituentsofthe exhaust gas.

Referring to FIG. 2, the casing 28 of the heat exchanger 16 is shown asa cylindrical body. The casing may be fabricated from two mating partsthat are held together by fasteners and a gasket (not shown). This wouldenable the casing to be opened rapidly for easy cleaning, while theinlet and outlet tubes remained connected to ducting. The casing servesto protect the fins located in the interior thereof. The casing alsoserves as the outer duct. The ability to open the casing also permitsbaffles discussed hereinafter to be moved thereby altering the flow pathof gas flowing through the exchanger. The inlet of the casing isindicated by 30 and a first inlet pipe 32 is seen to communicatedirectly with the inlet opening 30. The first inlet pipe 32 carriesclean air. A second inlet tube 36 is positioned concentrically inwardlyof the tube 32. Both inlet tubes are concentric with the axis of thecylindrical casing 28. The inner opened end 38 of the inlet tube 36provides entrance for hot automotive emission exhaust gas. As will benoticed, the inner end 38 of this tube extends inwardly of the inletopening 30 and as exhaust gas is delivered through the tube opening 38it becomes mixed with the air delivered through the tube 32. As

mentioned in the previous discussion, through mixing of these gases isextremely important to produce desired homogeneity of air and exhaustgas.

An annular cylindrical fin assembly 40 is concentri- 5 cally mountedwithin the casing 28. A resulting axial passageway 42 extends along thelength of the fin assembly 40. At the left end of the fin assembly is acoolant header 44 which is disc shaped and like the fin assembly 40 isaxially disposed within the casing 28. The

1O header 44 connects the left ends of coolant pipes that run throughthe fin assembly 40. A second coolant header is shown at 46. This headerdiffers from coolant header 44 in that it is divided into two concentricannuluses by a ring-shaped baffle 49. The inner annulus distributes thecoolant, entering the heat exchanger among the inner set of tubes, andflows to the left. The outer annulus collects the coolant flowing to theright through the outer set of tubes. Coolant flows out of the heatexchanger from the outer annulus. The fin assembly 40 is positioned inthe location shown by annular baffles or spacers 48 and 50. In additionto supporting the fin assembly in the illustrated position, the bafflesgovern the path of the gas mixture flowing through the fin assembly 40.By making the baffle 48 slideably adustable, variations in the flow pathcan be created.

Referring to FIGS. 3 and 4, the fin assembly 40 is seen to include aplurality of annular shaped fins 52 that are positioned inlongitudinally spaced relationship with respect to a central axis. Thefins 52 are parallel to each other and spaced sufficiently to resistclogging. Coolant tubes such as 54 run through the fins 52 therebyeffecting heat exchange between the hotter gases flowing around theexterior surfaces of the fins and the cooler coolant fluid runningthrough the tubes 54. The individual fins 52 may be arranged in ahelical orientation rather than the illustrated orientation. Referringonce again to FIG. 2, coolant liquid flows into coolant tube 56 andafter traversing the length of the fin assembly 40, the coolant isreversed at the head 44 and executes a reverse flow to header 46 andthen out through coolant tube 58. It should be noted that the coolantheader 46 is separated into inner and outer chamber so that they mayrespectively function for coolant inlet and coolant outlet tubes 56 and58. Thus the coolant flow is at all points symmetrical about the axis.The coolant tubes may be arranged so that multiple passes through thefins occur. In a preferred embodiment, a high flow rate of the liquidoccurs commensurate with a low pressure drop thereby reducing requiredpumping power.

As mentioned in the previous text, the coolant header 44 confronts theinlet of tubes 32 and 36 with a surface against which the inlet gasescan impinge. By so impinging, the gases mix further and increasehomogeneity. After this mixing, the gas mixture flows radially outwardlyalong the left passageway 61 where the air flow from tube 32 shears theflow in passageway 61 to again increase the mixing effect. As will benoted in the figure, the flow path is symmetrical about the axis at allpoints between the inlet and outlet of the heat exchanger. The gasmixture then passes through a second passageway 62 defined between theinterior wall of the casing 28 and the exterior surface of the finassembly 40. It will be remembered that a positive displacement pump isconnected to the heat exchanger outlet so that a continuous flow isinsured between the inlet and outlet.

As shown in FIG. 2, the gas mixture then flows radially inwardly throughthe individual fins of the fin assembly 40. The gas mixture containedbetween adjacent fins can be visualized as an annular disc. As the gasmixture flows through the fins, heat exchange is effected as well asadditional mixing of the original exhaust gas and air components. Thefirst section of the fin assembly 40 through which the gas mixturepasses is generally indicated by reference numeral 64. After the gaspasses through this fin assembly section 64 it collects in and flowsthroughthe axial passageway 42 where additional mixing is accomplished.The baffle 48 defines the section 64 and prevents the gas mixture fromflowing into an adjacent section 66 of the fin assembly prior to havingtraversed the passageway 42. After the gas mixture flows radiallyoutwardly through the fin section 66 it collects in a second annularcylindrical passageway 68 that further directs the gas mixture in alongitudinal direction. The baffle 50 restrains the longitudinal flowthrough the passageway 68 and forces the gas mixture to continue itsflow through a final fin assembly section 70. After passage through thefin assembly section 70 where the gas is mixed further, the gas mixturecollects in an axial passageway 74 that is adjacent the passageway 42and separated therefrom 'by an axial baffle 72. The final temperatureconditioned gas mixture flows through the axial opening 74 into an endpassageway '76 bounded between the right end of the casing 28 and theconfronting surfaces of coolant headers 46, 59 and the baffle 50.

The resulting radial flow path expands and contracts which alternatelyrarifies and compresses, accelerates and decelerates the flowing gas insuch a way as to dampen other pressure and velocity cycles, includingsound waves generated by associated machinery.

An outlet tube 78 is connected to the casing 28 and communicatesdirectly with the passageway 76. The inlet tubes 32, 36 and the outlettube 78 may be installed in a length of straight ducting by removing alength of duct equal to the length of the heat exchanger andsubstituting the exchanger for the duct section. A poppet valve assembly80 is positioned at the inward end of the outlet tube 78 to controloutlet flow. The poppet valve augments gas mixing by generatingturbulence and directional changes within the gas stream yet does notgenerate density strata in downstream ducting. Specific utilization ofthis valve will be explained hereinafter. However, as will be noticed,the embodiment illustrated in FIG. 2 presents the gas mixture with threepasses through the fin assembly 28 where the inlet gases are cooled andmixed. In addition, passageways or plenums present themselvesalternately between the passes, by the gas mixture, through the finassembly 28. Further mixing in these passageways occurs.

Thus, far, it should be appreciated that the described embodiment ofFIG. 2 exhibits a symmetrical flow pattern which maintains thermal andphysical symmetry that improves flow distribution and augments heattransfer and gas mix homogeneity. This symmetry also results in a zerostrat discharge gas flow that is suitable for sampling and analysis.Although the previous discussion referred to the liquid as a coolant,this need not be so. The temperature of the gas exiting from the heatexchanger is controlled by the fin and coolant tube temperature which inturn is maintained by liquid flowing through the tubes. This liquid maybe hotter or The valve assembly includes a poppet valve head 82 thatcooperates with the valve seat 84. The seat is formed in the left end ofthe outlet tube 78. An elongated valve stem 86 is axially disposed alongthe length of the outlet tube 78 and has threads 88 formed along anintermediate portion thereof. A mating threaded sleeve 90 supports thevalve stem 86 in its illustrated position, the sleeve 90 being itselfsecured to the outlet tube 78 by welding (92) or the like. A first 0ring 94 is located at the left end of the sleeve 90 and serves toprotect the interior threads from corrosive constituents of the exhaustgas. A second 0 ring 96 is located at the opposite end of the sleeve 90to achieve the same result. It is to be emphasized that other means maybe employed to mount the poppet valve member 82 in its illustratedposition. However, for purposes of clarity and brevity, the valvemounting members have been explained as set forth above. In order toadjust the seating of the poppet valve member 82, a driven gear 98cooperates with a mating driving gear 100 that is in turn driven bymotor 102. By energizing motor 102, rotational motion of the gears 98and 100 is translated to axial displacement of the poppet member 82.

As illustrated in the figure, the outlet tube 78 extends to a rightangle elbow portion 104 which terminates at a positive displacement pump(not shown) which draws the gas mixture through the heat exchanger.

The poppet valve assembly 80 is primarily utilized during calibration ofthe sampling system shown in FIG. 1. During calibration, pressuredifferential of the displacement pump versus volume displaced by thepump per revolution of a pump cycle is plotted over a range of valvepositions. This is repeated during a second calibration cycle and ifrepeatability is good and the plot compares favorably with apredetermined standard plot, the system is operating satisfactorily.

FIG. 3 illustrates an alternate embodiment of the present inventionwherein baffles are not used along an intermediate length of the finassembly 40. This produces a single pass of gas mixture through the finassembly 40, as illustrated. The disposition of an axial baffle orheader plate 106 immediately inwardly of the inlet causes mixing of thegas components introduced at the inlet, as previously described. Aplenum or passageway 108 directs the gas mixture radially outwardlywhere additional mixing takes place. Asecond path direction of the gasmixture is the annular cylindrical passageway or plenum 110. From thispassageway, the gas mixture flows radially inwardly through the fins 52of the fin assembly 40 during which time the gas mixture undergoes heatexchange and additional mixing. Finally, the gas mixture collects andflows axially through the central passageway 114 which communicatesdirectly with the outlet of the heat exchanger. An annular baffle 112 atthe right end of the fin assembly 40 restricts the longitudinal flow ofthe gas mixture. As clearly shown in FIG. 4, a number of spaced coolanttubes 54 pass through the individual fins 52 of the fin assembly 40.This is to achieve the most efficient and even heat transfer.

FIG. 5 shows an alternate embodiment of the present invention. In thisembodiment, the outlet tube is positioned at the same end of the heatexchanger as the inlet tubes. To add clarity to this figure, headerdetails and coolant pipes have not been shown.

More specifically, a cylindrical casing 116 is provided with aninteriorly disposed annular fin assembly 118 of the type previouslydiscussed. An outlet opening 120 is formed in the left end of the casing116. An elbow shaped outlet tube 122 communicates directly with theinlet opening 120. The opposite end of this tube is connected to apositive displacement pump which forces the temperature conditioned gasmixture through the heat exchanger. A second tube 124, which serves asan inlet tube, is positioned in inward concentric relation to the tube122. The tube 124 is connected to the left end of the fin assembly 118at point 128. An opposite end of the tube 124 passes outwardly at 126through the elbow tube 122. This second tube 124 carries clean air to bemixed with exhaust gas that is delivered to the heat exchanger by athird inlet tube 130. This latter mentioned tube is concentricallydisposed within the air inlet tube 124. The inward end of tube 130 isoffset from the left end of fin assembly 118, and as a result, the airflow shears through the exhaust gas flow, at the inlet plenum 132thereby mixing the gases. After this initial mixing of the gases, themixture travels through the axially located passageway 134. By applyingdisplacement pressure at the outlet tube 122, the gas mixture is drawnthrough the fin assembly 118. As the gas passes through the axialpassageway 134, additional mixing is obtained. Still further mixing isobtained as the gases pass through the individual fins of the finassembly 118. In addition, as previously explained, as the gas mixturepasses through the fin assembly heat exchanger is effected. The gasmixture collects in the axial cyclindrical plenum or passageway 134where once again mixing occurs. Finally, the gas mixture flows to theopening 120 where the mixture is delivered to the interior 136 of theoutlet tube 122. Reference numerals 137 and 138 indicate inlet andoutlet headers. Seals at 127 and 131 permits the removal of the casing116 without disturbing ducts and plumbing. Thus, access is provided tothe gas and liquid passages for cleaning purposes. A V-band clamp 129retains the seal 129 in place.

FIG. 6 illustrates an additional embodiment which is somewhat similar tothe embodiment of FIG. but represents a reciprocal arrangement of inletand outlet tubes.

Again, a cylindrical casing 140 surrounds an inwardly disposedcylindrical annular fin assembly 142. Annular baffles 144 and 146support the fin assembly 142 in its illustrated position as well asdefining the path through which the gas mixture is to flow. A largeinlet opening 148 is formed in the left end of the casing 140. An elbowshaped inlet tube 150 communicates directly with the opening 148. Theinlet tube 150 provides for the delivery of filtered air to the heatexchanger. A concentric and radially inward tube 152 has its inward endcoplanar with the inlet opening 148. An intermediate length of the tube152 passes outwardly through the elbow of the inlet tube 150. Thetube152 carries exhaust gas to the heat exchanger. A third concentric tube156 is positioned radially inwardly of the second mentioned tube 152. Asin the case of tube 152, the tube 156 passes outwardly through the elbowportion 154 of the inlet tube 150 while the inward end of the tube 156is attached to the left end of the fin assembly 142. The tube 156 isoutwardly connected to a positive displacement pump for drawing the gasmixture introduced at the heat exchanger inlet through the length of theexchanger.

In operation of the embodiment shown in FIG. 6, exhaust gas flowingthrough tube 152 is indicated at 162. Filtered air delivered by theinlet tube shears the flow of the exhaust gas and produces mixing of theair and exhaust gases. The coolant header surface 164 presents a mixingsurface as previously discussed in connection with FIG. 2 which causesfurther mixing of the gases. In order to add clarity to FIG. 6, theheader details and coolant tubes have been left out of the figure. Aninitial plenum or passageway 166 is created to cause the gas mixture toflow radially outwardly to the annular cylindrical passageway 168 whichdirects the gas mixture flow to a first section of the fin assembly 142.After the gas mixture has passed through this fin assembly section, itis collected in the axial passageway 170. As in the previously discussedembodiments, the gas mixture undergoes heat exchange as the mixturepasses through the fin assembly section. Additional mixing occurs in theaxial passageway 170 and by virtue of an annular axially positionedbaffle 176 the mixture is redirected through the fin assembly 142,through a second section thereof, until the gas collects in a secondpassageway or plenum 172. Additional mixing occurs and from thispassageway the gas flow is redirected once again through the finassembly 142, through a third section thereof. The placement of baffle146 inwardly from the right end of the fin assembly causes the gasmixture that has collected in the axial passageway 174 to flow onceagain through the fin assembly 142, through a fourth section thereof.Finally, the gas mixture traverses the plenum 178 and returns throughthe axial opening 180 to the outlet tube 156. Thus, the embodiment shownin FIG. 6 effects four passes of the gas mixture through the finassembly.

In each embodiment, the heat exchanger casing is designed to allowsimple removal so that the fin assembly and other interior componentsmay be cleaned and inspected. Deep drawn stampings make light casingswhich contribute to compact outside dimensions for a given fin assemblyheat transfer surface. The radial flow at the ends of the casingeliminates the need for large distribution plenums. Therefore, not onlyis the heat exchanger compact, but its installation is compact as well.The casing, fins, and coolant tubes can be made of any material desiredso that the exchanger can be subjected to extreme temperatures andchemicals. Once again, it is reiterated that the invention contemplatesthe ability to add or remove baffles so that the number of passes by atemperature conditioned gas mixture can be altered after the heatexchanger is built. This ability is an advantage many heat exchangerslack.

All passes of the mixtured gas are symmetrical because the heatexchanger is cylindrical. Flow is alternately axial and radial butalways symmetrical about the center line of the heat exchanger. Thesymmetrical flow improves flow distribution which augments heat transferand gas mix homogeneity.

The coolant flow path for a particular embodiment is not restrictive.Thus, coolant flow may be reversed from the directions shown, such as inFIG. 2. The coolant tubes may be manifolded with tube fittings, fed fromheaders as shown, or may form a series flow path. The fin structure maybe varied so that it includes a serpentine" arrangement of fin tubeswhich may be wrapped in any-convenient manner to form the fin assembly.

By having the flow as constituting an alternate series of radial andaxial directions, the line of sight transmission of noise from thedisplacement pump is blocked.

Although the figures have been discussed in terms of multiple inletgases, it is essential to note that the heat exchanger embodiments shownwill also achieve superior heat exchange with a single inlet gas.

It should be understood that the invention is not limited to the exactdetails of construction shown and described herein for obviousmodifications will occur to persons skilled in the art.

Wherefore, we claim the following:

1. A heat exchanger having a housing and comprismg:

a heat exchanger fin assembly symmetrically mounted in the housing, thefin assembly including an annular cylindrical body comprisedof axiallyspaced fin members, the assembly being radially spaced from the housing;

inlet means having a plurality of concentric inlet tubes connected tothe exchanger for delivering respective fluids to the exchanger,simultaneous entry of the fluids causing turbulent mixing of the fluidsto occur;

a first axial passageway formed between the fin assembly and the housingto alternately direct the flow of mixed fluids radially and axiallybetween the inlet means and an outlet means;

a second axial passageway being formed along the axis of the finassembly; the fluid mixture alternately flowing between the first axialpassageway, the annular space between the individual fin members, andthe second axial passageway;

coolant means connected to the fin assembly for effecting desired heattransfer between the fin assembly and the fluid mixture, resulting intemperature conditioning of the fluid mixture which is homogeneous whendelivered to the outlet means;

at least one annular baffle to block the first axial passageway at apreselected point therealong; and

at least one baffle disposed at a preselected point along the secondaxial passageway;

the presence of the annular and axial baffles forcing the fluid flow tomake several passes through the fin assembly between the inlet andoutlet means thereby increasing the temperature conditioning of thefluids and the homogeneity thereof.

2. The structure of claim 1 wherein the coolant means further include atleast one header for manifolding a plurality of coolant tubes passingthrough the fin members, the header having a mixing surface adjacent theinlet tubes against which the inlet fluids impinge.

3. The structure of claim 1 wherein at least one preselected baffle isremovably mounted within the exchanger.

4. The structure of claim 1 wherein an adjustable number of baffles arelocated within the exchanger, the

number of baffles commensurately changing the number of passes acrossthe fins.

5. The subject matter of claim 1 wherein the outlet means includes:

a plenum; and valve means interposed between the plenum and an outletpipe for symmetrically throttling the gas flow through the exchanger andfor generating turbulence in the gases as they pass across the valvethereby enhancing mixing of the gases. 6. The subject matter of claim 1wherein the inlet means includes an inlet plenum for receiving inletgases and further wherein the header is aligned with the plenum forcausing impingement of the inlet gases thereagainst thus redirecting theinlet gases through the exchanger in a turbulent manner to enhance themixing of the gases.

1. A heat exchanger having a housing and comprising: a heat exchangerfin assembly symmetrically mounted in the housing, the fin assemblyincluding an annular cylindrical body comprised of axially spaced finmembers, the assembly being radially spaced from the housing; inletmeans having a plurality of concentric inlet tubes connected to theexchanger for delivering respective fluids to the exchanger,simultaneous entry of the fluids causing turbulent mixing of the fluidsto occur; a first axial passageway formed between the fin assembly andthe housing to alternately direct the flow of mixed fluids radially andaxially between the inlet means and an outlet means; a second axialpassageway being formed along the axis of the fin assembly; the fluidmixture alternately flowing between the first axial passageway, theannular space between the individual fin members, and the second axialpassageway; coolant means connected to the fin assembly for effectingdesired heat transfer between the fin assembly and the fluid mixture,resulting in temperature conditioning of the fluid mixture which ishomogeneous when delivered to the outlet means; at least one annularbaffle to block the first axial passageway at a preselected pointtherealong; and at least one baffle disposed at a preselected pointalong the second axial passageway; the presence of the annular and axialbaffles forcing the fluid flow to make several passes through the finassembly between the inlet and outlet means thereby increasing thetemperature conditioning of the fluids and the homogeneity thereof. 2.The structure of claim 1 wherEin the coolant means further include atleast one header for manifolding a plurality of coolant tubes passingthrough the fin members, the header having a mixing surface adjacent theinlet tubes against which the inlet fluids impinge.
 3. The structure ofclaim 1 wherein at least one preselected baffle is removably mountedwithin the exchanger.
 4. The structure of claim 1 wherein an adjustablenumber of baffles are located within the exchanger, the number ofbaffles commensurately changing the number of passes across the fins. 5.The subject matter of claim 1 wherein the outlet means includes: aplenum; and valve means interposed between the plenum and an outlet pipefor symmetrically throttling the gas flow through the exchanger and forgenerating turbulence in the gases as they pass across the valve therebyenhancing mixing of the gases.
 6. The subject matter of claim 1 whereinthe inlet means includes an inlet plenum for receiving inlet gases andfurther wherein the header is aligned with the plenum for causingimpingement of the inlet gases thereagainst thus redirecting the inletgases through the exchanger in a turbulent manner to enhance the mixingof the gases.